DE 36 36 321 A1 shows an arrangement and a method for determining the state of wear of a component.
An arrangement of the abovementioned type is known, for example, in the context of a combustion chamber of a gas turbine. The combustion chamber has an interior space and a housing surrounding the interior space. A fossil fuel is burnt in the interior space of the combustion chamber. A temperature of up to 1500° C. is reached during the combustion. Corrosive gases are also produced and attack the housing of the combustion chamber. To protect the housing from the high temperatures and from attack from corrosive gases, the combustion chamber is lined with a large number of what are known as ceramic heat shields.
A heat shield is a component formed from a component material which has a very good resistance to temperature and corrosion. The component material is, for example, a ceramic material in the form of mullite. On account of a porous structure with a multiplicity of microcracks, the ceramic material has very good thermal shock properties. A very strong temperature fluctuation, as occurs, for example, in the combustion chamber of the gas turbine when the combustion process is interrupted, is compensated for without the heat shield being destroyed. However, in the event of a mechanical overload of the heat shield, the heat shield can be degraded. A crack (macrocrack) can form in the heat shield. A crack of this nature forms in particular at an edge of the heat shield. In operation, the crack can propagate toward the center of the heat shield. Up to a certain length, the crack has no adverse effect on the ability of the heat shield to function and can therefore be tolerated. However, if the crack exceeds a defined length, the ability of the heat shield to function is no longer ensured. It is necessary to replace the heat shield in order to avoid fracture of the heat shield caused by the crack while the gas turbine is operating. It is therefore absolutely imperative that the existence of a crack be detected and that the length of the crack be determined.
The recording of the crack or the length of the crack in the heat shield is carried out during a stationary phase of the gas turbine with the aid of an inspection device for optical recording of the crack. The recording is generally carried out from the interior space of the combustion chamber. An optically accessible surface portion of the heat shield which faces the interior space of the combustion chamber is inspected. On the other hand, if the rear surface of the heat shield is to be inspected, this can often only be done by dismantling the heat shield. The rear surface is a surface portion of the heat shield which is remote from the interior space of the combustion chamber. The method which has been demonstrated for recording the degradation and therefore for checking the ability of the heat shield to function is very time-consuming and therefore expensive.